The episode opens with Cat looking up at the floating Supergirl, who says she's ready to answer whatever questions Cat has.
Cat asks here where she is, and is nonplussed when she has the same backstory as Superman's. The two banter back and forth and eventually Kara slips up and reveals she's Superman's cousin. She flies off while Cat shouts questions after her.
Later, at a diner, Kara eats sticky buns at breakfast. Both Alex and James show up to meet her. Kara flirts with James, and Alex is suspicious. Kara protests that they're "just friends," but Alex isn't buying it. She also wants people to stop telling people about Supergirl. Of course, that's when the report comes on TV that Cat has revealed her relationship to Superman.
At the office, Cat wants to write an expose on Supergirl. Kara is surprised to hear it, but Cat says she's a writer, so why not? They're going to do a special edition of their monthly magazine, and will throw a huge party to launch it.
Elsewhere, a man with facial disfigurement is watching a news report. When he sees that Kara is Supergirl's cousin, he suits up in an armored outfit and blasts the TV.
At the DEO, neither Henshaw nor Alex are happy that Kara gave the interview. While they're talking about it, the DEO gets a "code grey." As they're scanning for signs of alien life, Kara vanishes to go help.
Arriving at the scene of a pile-up on the highway, Supergirl has to go inside a bus and rescue the driver, who has been pinned inside the vehicle. She saves the woman, and gets blasted immediately after by the armored man -- Reactron. He wants to kill Supergirl to get to Superman. The two fight briefly and while he's no match for Kara physically, he keeps hitting her with energy blasts that keep her back on her heels until she throws a car door at him, damaging his armor and cutting off his blasts. He takes to the sky to escape.
At the DEO, Henshaw says they can't help Supergirl with Reactron because he's human, just using advanced tech, and not an alien.
Back at work, Kara comes to see Cat about party details. Cat is having trouble writing the story.
Outside her office, Winn and James meet her and take her down the hall to a vacant office in the building, where he's set up a Team Supergirl cave. James wants her to call Superman for help, calling him Clark, which makes Winn crazy. She says she can't call him for help or it will make her, and the city, look like an easy target.
At Lord Technologies, CEO Maxwell Lord fires an engineer who has been working on a project for three years but didn't figure out something he wanted. He walks off, talking about the appeal of a high-speed light rail when Reactron comes in looking for someone who can help him understand nuclear fission. He tries to kidnap a scientist, but Lord stops him and volunteers himself.
Upon hearing on the news about the attack, Supergirl takes off, but by the time she arrives, Reactron and Lord are both gone.
When Team Supergirl are talking about what they're going to do, Alex shows up to offer assistance. They figure out that Reactron was a nuclear technician at a reactor that nearly melted down. Superman saved it and millions of lives, but two people died -- a man and his wife. Turns out, the man didn't die, and now he's Reactron. At Reactron's lair, Max Lord offers to help Reactron get a normal life back, but Reactron doesn't want it; he wants a new suit so that he can keep going after Superman. Lord agrees.
At CatCo, Kara is the first one to read Cat's Supergirl story. She thinks the writing is great, but doesn't like the fact that she's attacking Supergirl. Kara tells Cat that she's being unfair to Supergirl, but Cat isn't buying it. James comes in to talk to Kara, bringing her outside. Winn has located Reactron, and Kara plans on going to find him and trying to reason with him. She heads to a junkyard where Maxwell Lord is tied up. When she tries to free him, Reactron pops out and attacks her. She tells Lord to run, and he does. She tries to reason with Reactron, who attacks her relentlessly. When she's down and he's ready to attack again, Superman arrives and takes the blast, saving her.
At home later, Kara wakes up. Alex and James are there. Superman had to leave while she was out. Maxwell Lord is on TV, thanking Superman for saving him. James used his signal watch to call Superman, and Kara is not happy about it. After James leaves, Kara has to go to the party.
There, she is chewed out by Cat, then dances with Winn. Meanwhile, Maxwell Lord and Cat Grant flirt a bit. He asks about her connection to Supergirl. Cat teases him a little, then leaves the party early.
At the DEO, Henshaw's eyes light up, and he says Alex's name. He walks into a forensics lab to see her and confronts her about helping Kara. She says she can't separate alien threats from human ones. Henshaw asks her who else knows she's been using DEO facilities to help Kara. She says no one and he says good, but asks how to defeat Reactron.
At the party, James comes and tells Kara that Superman wasn't her safety net: he's Olsen's. He uses the watch when he gets scared, and that's part of why he left Metropolis. She tells him she needs his trust, and James says that he does trust her, he's just worried about her sometimes.
Reactron crashes in through the ceiling, demanding to know where Supergirl is, and fires off a blast at a nearby poster with her picture on it as the crowd scatters.
As Reactron is about to go after Lord, Supergirl comes through the ceiling and kicks him to the ground. He threatens, and then blasts, her before a stray shot takes out a beam and almost kills Winn. As Supergirl saves him, James distracts Reactron by holding himself up as a potential victim. Reactron follows him out of the building, while Alex calls to Kara and tells her that taking out Reactron's chestplate will render him powerless, but it will melt down immediately. She needs to cover it in lead first. Kara melts part of a lead statue onto her hand and heads outside to battle Reactron. successfully removing the power core from his chest plate with her lead-covered hand, she looks around to find James, chastising him for putting himself at risk, but he says he knew she would save him.
At the DEO, Supergirl thanks Henshaw and Alex for their help. Henshaw says he guesses they're in the Supergirl business from now on. When Alex asks Kara's plans for the night, Kara suggests a movie night with her sister but Alex tells her to ask out Jimmy instead.
At Jimmy's office, his ex-girlfriend Lucy Lane is there, and he asks to be left alone with her. She spies on them, with Lucy asking him to get dinner and talk. Jimmy says OK, although neither of them seems happy about it. Kara is really upset. She goes back to her desk, where Winn asks her what's wrong and she blows him off. There, she gets a text from Clark. She thanks him for the rescue, and Clark says it won't happen again, and then tells her she's doing great.
Later, at Alex's apartment, Alex tells Kara that she read Cat's story and that she can tell Cat secretly respects Supergirl. She takes off out the window at the sound of a siren.